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ATTM NEY Patented Dec. 23, 1 952 SINGLE CHANNEL,

SINGLE FREQUENCY,

MOBILE RADIO TELEPHONE SYSTEM Roswell H. Herrick, Lorain, Ohio, assignor to Automatic Electric Laboratories, Inc., Chicago, Ill-., a corporation of Delaware.

Application November 1, 1948, Serial No. 57,764

11 Claims.

The present invention relates to telephone systems in general, and more particularly to radio telephone systems wherein radio transmitters and receivers are employed for establishing telephone connections between ordinary immobile stations of a telephone exchange system and mobile station units such as automobiles. boats and the like. Y p

It is an object of the invention to provide a telephone system of the character described, in which system connections in either direction are automatically established in. a new and novel manner by the dialing of the regular directory rtiiumbers of the wanted immobile or mobile staons.

Another object of the invention is to provide in a telephone system of the character described, selective signalling and secret service between immobile and mobile stations in eithe direction over a single radio channel.

A further object of the invention is to provide a simplified telephone system of the character described, wherein the dial impulses from a calling station are received as splashes" of tone modulation of the incoming radio carrier, and are delivered from the radio receiver as corresponding splashes of tone of a single frequency.

A still further object of the invention is to provide in a telephone system of the character described, new and novel circuit means for establishing the various telephone connections.

A feature of the invention resides in the novel arrangement wherein only four conductors are combined between the telephone exchange and the fixed radio control station for the transmission of impulses, tone signals, speech, and superviso'ry and other control circuits.

Another feature of the invention relates to the novel manner in which the radio transmitter of a mobile station unit is automatically switched oil the air in approximately two seconds after the initiation of a call at that unit.

A further feature oi the invention is that the output circuit of the radio receiver at each mobile station unit is normally connected to the incoming tone detector circuit".

A still further feature of the invention is that the impulse receiving relay of the incoming tone detector circuit at each mobile station unit is operated by rectified power from its radio receiver.

Another feature or the invention concerns the selective excitation of the tone oscillator and the tone detector at the fixed radio control station on outgoing and incoming calls respectivelyc Another feature of the'finvention is'the immediate locking out units responsive to the placing of the transmitter carrier of the fixed radio control statio'mon the air on the initiation of a call by an immobile station. a

Another feature of the invention is that the seizure of the receiver oithe fixed radio control station responsive to the receipt of the carrier from the radio transmitter of a calling mobile station unit causes the transmitter carrier of. the fixed radio control station to be placed on the air in acknowledgment, which results in the looking out of all the mobile station units except the calling mobile station unit.

Another feature of the invention is the provision of an auxiliary operating circuit for the squelch relay at each mobile station unit to hold the squelch relay operated on an established connection during the talking periods at the mobile station unit when the radio receiver is disabled and the radio transmitter is on the air.

Another feature of the invention is a novel 'call (conversation) timer which disables an established connection when the timed interval lapses.

Another feature of the invention is that on a call from a mobile station unit to an immobile station, a motor-operated timer in a new and novel manner automatically causes the restoration of the control circuit at the fixed radio control station, should the dialing of the immobile stations number and the answering of that station not be accomplished within the timed interval.

switching-through relay Another feature of the invention relates to the novel manner in which temperature-controlled resistors are utilized as timers for controlling various operations of the equipment.

Another feature of the invention concerns the novel use of a slow-to-operate relay in the impulse receiver circuit of all mobile station units for preventing possible false operation of the of all the mobile station Other objects and features will become apparent from the following specification together with the accompanying drawings which show a proposed embodiment by way of example.

The invention is disclosed in five sheets of drawings comprising Figures l-A, 1-13 and 1 to inclusive.

Figure l-A shows in block formation an automatic telephone exchange accessible to a group of subscribers, such as T, and the switching apparatus whereby the subscriber T may make or receive calls through the trunk repeater 49.

Figure 1-3 shows the two-way repeater 49 associated with the automatic exchange 1 whereby incoming and outgoing calls may be automatically extended between the control circuit 300 at the fixed radio control station and the automatic exchange I.

Figure 1 shows the auxiliary equipment required at the automatic telephone exchange for connecting the automatic telephone exchange to the fixed radio control station. 8

Figures 2 and 3 when placed side by side show the equipment and arrangement of the control circuit 300 at the fixed radio control station.

Figures 4 and 5 when placed side by side show the equipment and arrangement of one of the mobile station units.

Telephone ofiice switching equipment Figure 1-A shows subscriber line 2 extending to substation T and a line circuit 1 individually associated with line 2. The automatic switching apparatus comprises a plurality of groups of finder-selector links, each provided with an associated distributor, and which correspond with the groups of subscriber substations. One of the groups of finder-selector links includes a finder I0 and the selector II, and is provided with an associated distributor 9 common to the group; which group of finder-selector links is associated with the group of subscriber substations including the substation T. Also the-automatic switching apparatus comprises a plurality of groups of connectors respectively associated with the groups of subscriber substations. One of the groups of connectors includes the connector 22, and is associated with a group of subscriber substations including substation T. The automatic switching apparatus further comprises a roup of incoming selectors including the incoming selector 24. More particularly, finder I0 of the finder-selector link illustrated has access to line 2 extending to substation T; while selectorv II of the finder-selector link illustrated has access to connector 22 by way of the associated trunk 2I. Also, selector II has access to outgoing trunk I2 extending into the trunk repeater circuit 49; while incoming trunk extending from the trunk repeater circuit 49 is terminated in incoming selector 24. Finally, incoming selector 24 has access to connector 22 by way of associated trunk 2I. Preferably the finders I0, the selectors II, the selector 24, and the connectors 22, are two-motion stepping switches of the well-known Strowger type, but not necessarily. It should also be understood that while only one rank of selectors is shown, indicating a thousand-line office, the insertion of intervening ranks of selectors would readily expand it to a larger size.

Referring to Figure 1-3, trunk repeater 49 there illustrated has a set of conductors I4, I5 and I6 comprising trunk I2 which is accessible to selector II. Conductors I4 and I5 are normally connected through repeater 49 to talking conductors HI and I12 which extend to the telephone ofiice auxiliary equipment I19. The trunk repeater 49 further comprises a signal-in relay III! which is effective to repeat impulses received from a mobile unit, over the telephone ofiice auxiliary equipment I19, to incoming selector 24 over conductors I1 and I8 of trunk circuit 20.

Telephone ojfice auxiliary equipment Figure 1 shows the telephone ofiice auxiliary equipment connecting the automatic switching equipment (Figures l-A and l-B) in the telephone ofiice to the radio station control circuit 300 (Figures 2 and 3). This auxiliary equipment is usually located in the telephone omce building but may be located at a remote point if circumstances so require. The automatic switching equipment is connected to the auxiliary equipment by talking conductors HI and I12, by out line simplex signal conductor I19, and by in line simplex signal conductor I13. The auxiliary equipment is connected to the radio station control circuit 300 by conductors I and I9I which constitute the out line talking conductors and by conductors I94 and I which constitute the in line talking conductors.

The auxiliary equipment comprises essentially a hybrid transformer I83 and an associatedbalancing network I86 consisting of an adjustable resistor I81 and a capacitor I88. The transformer I83 serves to. efiect the separation of incoming and outgoing voice currents as necessitated by the inherent one-way characters of the radio transmitterand radio receiver. The talking conductors I11 and I12 from the automatic switching equipment extend to the lefthand winding of repeating coil I14 and, at this point, voice currents from the automatic telephone office are induced into the right-hand winding of repeating coil I14. Talking conductors I15 and I16'connect the right-hand winding of repeating coil I14 .to the upper and center windings of transformer I83, and, at this point, voice currents from .the automatic telephone office through repeating coil I14 are induced into the lower windings of transformer I83. Talking conductors I11 and "8- extend from .the outer terminals of the lower windings of transformer I83 through break contacts I5I and I54 of key I50 to conductors I90 and I9I constituting the out line talking circuit to the radio station-conv trol circuit 300. Repeating coil I14 provides line balancing meansfor minimizing disturbances resulting from excessive power line exposure of the telephone lines. The .out line simplex signal conductor I10 from the automaticswitching equipment extends to the center tap of the lower winding of transformer I03.

Conductors I94 and I95 comprising the in" line talking circuit from the radio station control circuit 300 extend to the right-hand winding of repeating coil I93 and, at this point, voice currents from the radio station control circuit 300 are induced into the left-hand winding of repeating coil I93. Talking conductors I8;I and 182 extend from the outer terminals of repeating coil I93 to the center taps of the upper and center windings of transformer I83, and voice currents .from the radio station control circuit 300 are transmitted through the left-hand upper and center windings of transformer I83 to conductors I15 and I16 extending to the righthand winding of repeating coil I14. At this point, voice currents from theradiqstation com trol circuit are induced into the left-hand winding of repeating coil I'll to conductors III and I12 leading to the automatic switching equipmentin the telephone ofiice. The in line simplex signal conductor I13 from the automatic switching equipment extends through break contact I58 of key I50 to the inner terminals of the right-hand winding of repeating coil I93 by way of the two windings of relay I I0.

The auxiliary equipment also includes a timing arrangement for controlling simulated second" dial tone and simulated ring-back tone on calls outgoing from the telephone offlce to a mobile unit. In addition to relay IIO, this timing arrangement includes relays I20 and I30 and the associated temperature-controlled resistors I25 and I35; which function in a manner to be described later in this specification. Continuous ringing voltage is supplied from the automatic switching equipment over conductor I23 and through capacitor I24 to relay I20, and interrupted ringing voltage over conductor I33 and through capacitor I34 to relay I30.

Monitor jacks connected to the talking conductors of the auxiliary equipment provide means for monitoring calls between the telephone oflice and the mobile units. Jack IOI is bridged across the talking conductors of the automatic switching equipment: jack I02 is bridged across the in line talking conductors from the radio station; and jack I03 is bridged across the out line talking conductors to the radio station. All three jacks are connected with suitable resistors in each conductor to maintain line balance and to prevent appreciable effect on an established conversation when monitor equipment (not shown) is pluggedinto any one of the monitor jacks.

A two-way test key I50 is also incorporated in the auxiliary equipment. The right-hand portion of th key provides facilities for determining whether or not there is a connection established between the telephone office and a mobile unit. The left-hand portion of the key provides means for turning the equipment of radio station control circuit 300 (except power transformer 303) on or off, as the case may be.

Temperature-controlled resistors are employed in the timing arrangement, for delaying the operations of relays I20 and I30. Each of these resistors has a relatively high normal (cold) resistance through which the associated relay cannot operate, but during a predetermined period of heating, the resistance is gradually lowered sumciently to permit the relay to operat at the desired time.

Radio station control circuit Figures 2 and 3 show the arrangement of the radio station control circuit 300. This equipment interconnects the automatic switching equipment (Figures l-A and l-B) in the telephone ofiice and the mobile units (such as illustrated in Figures 4 and 5) of the channel, by way of the auxiliary equipment (Figure 1) in the telephone ofiice and transmitter 30I (Figure 3) and receiver 328 (Figure 3) at the radio station. The auxiliary equipment (Figure 1) is connected to radio station control circuit 300 by conductors I9 and I9I which constitute the out line talking conductors and by conductors I94 and I95 which constitute the in" line talking conductors.

An out line simplex signal conductor 293 extends from the winding of impulsing, or line, re-

lay 355 (Figure 3) to the inner terminals of the left-hand winding of repeating coil 236 (Figure 2) through the two windings of relay 2 I0. Relay 355 is operated responsive to dialled impulses received from the automatic switching equipment over out line simplex signal conductors. I10 and 293 for causing radio station transmitter 30I to be placed on the air, and for connecting the output circuit of tone oscillator 389 to the input circuit of transmitter 30I, alLin the manner to be explained in detail later in this specification.

An in! line simplex signal conductor 291 extends from tone detector 393 (Figure 3) to the left-hand winding of repeating coil 231 (Figure 2) through contacts of relays 310, 340, 2I0 and 220. The operation of the in line simplex signal circuit is detailed in a later section of this specification.

Radiostation transmitter 30l (Figure 3) which may be of any well-known type of radio transmitter suitable for the purpose, co-operates with radio receivers, such as 400 (Figure 4), of the mobile units over a common carrier channel. Radio transmitters, such as 40I (Figure 4), of the mobile units are tuned to a common channel with radio station receiver 328 (Figure 3), which maybe of any suitable well-known type. The audio frequencies incoming to radio station receiver 328 from a mobile unit pass over in line circuit 333, attenuator 338, band pass filter 339, and repeating coil 231 to in line talking conductors I94 and I95 leading to the telephone ofiice auxiliary equipment.

Attenuator 338 permits adjustment of the radio station output to the relatively high level (approximately 50 milliwatts) required for positive operation of tone detector 393, and also to deliver the nominal level of approximately 20 milliwatts maximum to the in line circuit. Band pass filter 339 provides means for rejecting noise and other frequencies below 300 and above 2600 cycles to improve the overall signal-to-noise ratio of the circuit.

Monitor jacks connected to the talking conductors of radio station control circuit 300 provide means for monitoring calls between the telephone oflice and the mobile units. Jack 3I8 is bridged across the in line talking conductors from the radio station receiver 328: jack 20I is bridged across the in line talking conductors to the telephone oflice auxiliary equipment beyond repeating coil 231, band pass filter 339, and attenuator 338: jack 202 is bridged across the out line talking conductors from the auxiliary equipment just ahead of repeating coil 238; and jack 3I'I is bridged across the out line talking conductor to radio station transmitter 30I beyond repeating coil 238 for monitoring the radio station transmitter modulation input. All four jacks are connected with suitable resistors in each conductor to maintain line balance and to prevent appreciable efiect on an established conversation when the monitor equipment (not shown) is plugged into any one of the monitor jacks.

The radio station control circuit 300 also includes cut-oil jacks for splitting the in line circuit and the out line circuit for testing or like purposes. The insertion of a plug (not shown) into jack 203 splits the in line circuit towards the auxiliary equipment, while the insertion of a plug (not shown) into Jack 204 splits the in line circuit towards the radio system. The insertion of a plug (not shown) into jack 205 splits the out line circuit towards the auxiliary equipment, and the insertion of a plug (not shown) into jack 206 s'plitsthe "out line circuit towards the radio system.

Supervisory lamp signals areincorporated 'in control circuit 300 for enabling maintenance personnel at the radio station to note-the operating condition of the circuit. Lamp 306 function's-to indicate that the main power supply is beingreceived. Lamp 301 functions to indicate-that radio transmitter 30! has been started, whereas lamp 308 functions to indicate *that the transmitter carrier is actually on the air. With the trans'm'itter radiating properly, bothlamps -301and' 308 glow simultaneously. Lamp Md-functions to-im dicate the remotely controlled on and 011" condition, glowing when the on condition exists, and dark when the off condition exists.

Transformer 303 'is the only power transformer in control circuit 300 normally active, even though the rest of-the-equi-pment 'inc'oritrol-circuit 300 may be turned off. Transformer-303 can be made inactive only by the operation of master switch 305,*which operation disconnects the main power supply (for example llfivolts. do-cycle, single phase A.-C.) to control -circu'it300 and thereby renders the entire radio station equipment dead. Transformer303 suppliesdirect current to ratchet switch-3 l2 (which isother-wise controlled to turn the radio-station equipment, except transformer 303, onf' or oif-) through the simple'half wave rectifier 3 f8.

Test switch 3 I is a facility which-'permitspersonnel at the radio station to start radio transmitter 30| locally. Since switch 3l0'is'preferably of the locking type (to permitmeasurement on the transmitter without requiring that switch 310 be held operated) pilot lamp309 functions'to'indicate that switch 3l0 shoul'db'e restored asquickly as possible. Test switch 3 Wprovidesmeansfor'the local operation of ratchet'switch 3l2thereby'to turn the equipment (except transformer 303)"'of control circuit 300"on" or oif as the "case may be.

Master switch 305 is a facility 'whichiplaces on-off control-of all'radio station'equipment, including transformer "303, in the hands of maintenance personnel at the radio staticmprimarny for personal safety. By-this control, 'a maintenance man makes the entireradio station equipment dead in order'to protect himself "while working on portions of the equipment "which would endanger him if unexpectedly energized. Pilot lamp 306 glows whenever masterlswitch 305 is in the closed position andrthere'fore when darkened by the opening of switch 3'05serves to indicate that switch 305 should be closed as quickly as possible to re-establish normal operating conditions.

Control circuit 300 further includesa-source of 48-volt (nominal) direct current and-asource of 250-volt direct current. The 48-volt direct current supply may be a conventionaldry-disc rectifier 33I with an inductive type of inputrsmoothing filter 332, ope'ratingfromtransformer-329. The 48-volt direct current thus i-madeavail'able is utilized for operating the various relays 'atthe radio station and certain of the pilot-' l'amp signals. The 250-volt direct current supply-may be a conventional tube rectifier using a '5Y3'GT/G vacuum tube 330 with a small-capacity type of tone oscillator 389. A winding 326 of transformer 321 supplies the heaters of 6SN'1GT tube' 320,

, I I a I q o supplyfor transmitter 40 I.

one section of which is the tone detector. and

the other'section the tone oscillator.

Mobile station units Figures 4 and 5-show the arrangement'and wiring of one of the'mobile units, and more specifically "may be subdivided-into dash control equipment'shown to the right of Figure 5 radio transmitter '40 l and radio receiveriM-s'hown totheleft of Figure i: incoming tone 'detectorcircuit comprisingrectifier 4 l 1, capacitor "429," and pulse-relay 5'45: tone "oscillator 489: impulse receiver shown to the left'of'Figure 5': and call timing equipmentIshown below the'centercf'Figure 5. I

The dashcontrol'equipmen-t comprises a telephone handset '50l a cradleswitch 503associated with handset 5!, an impulse dial 510, a master on-ofl switch 538, a buzzer .508, and supervisory pilot lamps'501,'5l3 and M0. Lamp 501 glows whenever handset 5! is off the'cradle: lamp 5|5 glows as an indication that master switch 538 has been operated to place mobileunit 500 in the standbycondition; andlamp 5l9'glows as an indication that the radio "channel is in use (busy). Buzzer 508 serves .as an audible "alarm that the mobile unit is out-of-range of the radio station.

The dash control equipment:is-mountedwithin easy reach and observation of the operator of the mobile unit. The transmitter and receiver control equipment may be located in any convenient space of the mobileunit which is accessible for inspection and adjustment .of this equipment.

Oneantenna is provided'for'the alternate use of radio receiver 400 and radio transmitter 40!.

Radio receiver 400 'isnormally connected'to the antenna through break contacts of a TL relay 405 which, when operated, switches the antenna from receiver 400 to transmitter 40!.

Radio receiver 400 may be of any suitable wellknown type and is responsive toreceipt of the carrier wave from transmitter30l of'the radio station to operate an associated squelch relay 0 for preparing the impulse receiver circuit and the call timing circuit. The output circuit of receiver 000 is normally connected to the incoming tone detector circuit by means of whichthe tone splashes from transmitter 30| of the radio station are relayed to the impulse receiver circuit of the mobile unit.

Radio transmitter 40| may be of any suitable well-known type, is normally disconnected from 'dialed impulses from dial 5l0) inthe form of tone splashes to the radio modulation circuit (not'shown) of transmitter 40! from which they are transmitted as modulations" on theoutgoing carrier.

The radio transmitter circuit also-includes a power relay 435 controlled by cradle switch 503, for starting and stopping a dynamotor 431. The dynamotor 431 is'the source'of the high voltage Thesaidtransmitter 1. .9 responds instantly to the application of the high voltage to place the carrier or the mobile uni-t on the air when TL relay 405 switches the transmitter to the antenna.

The call timing equipment comprises relays 580 and 590 and related resistors for timing two-way connections and for causing the break down of such connections should the conversation period extend to the limit of the timed period.

Temperature-controlled resistors are employed for delaying the operations of certain relays in the control circuit of mobile unit 500. Each resistor has a relatively high normal (cold) resistance through which the associated relay cannot operate, but during a predetermined period of heating, the resistance is gradually lowered sufficiently to permit the relay to operate at the desired time. a v

The impulse receiver includes a minor switch of well-known typeh'aving two wipers and associated -point contact banks for responding to the digits dialed by the calling person at the telephone office station to either (1) selectthe dash control equipment and signal the operator of the mobile unit by means of buzzer tone, should this mobile unit be the one dialed by the calling person, or (2) to continue the'lo'cked out condition of the mobile unit should the dialed digits correspond to another mobile-unit.

It should be understood at this time that while a plurality of battery connections are'shown in the drawings, they are preferably the same battery for the particular'unit of equipment. Also, in order to simplify the drawings further, contacts for starting and stopping the operation of the ringing carrier generating equipment have been omitted. An X contact shown-in association with a relay armature is a contact that makes or breaks before any other contacts of the particular relay are closed or opened, thus characterizing the relay as a two-step relay.

Having described the equipment and apparatus, a detailed description of the operation will now be given.

Placing equipment in standby condition The equipment associated with radio station control circuit 300 and the mobile units (such as 500) are maintained in a normal standby condition preparatory for use. Essentially, the standby condition involves maintaining the receivers at the radio station and the mobile units-in the fully operative state and the tube heaters of the radio station transmitter energized. Subsequent completion of the high voltage (anode) circuit of the radio station transmitter will, therefore, instantaneously place this transmitter on the air. In the mobile units, the 'radiotransmitters utilize tubes of the filament quick-heating type thereby .to reduce standby power'requirements.

In the radio station control'oircuit-300, the standby condition requires additionally a direct current battery supply or 48 volts (with a grounded positive terminal) for relayoperation and for' certain supervisory lamp operations: a direct current supply or 250 volts for the anodes of tone oscillator 389 and tone detector 393; and the energization of the heater supply for the combination tube in the tone oscillator 389 and the tone detector 393.'

The first step in establishing the standby condition at the radio station is the closing of master switch 305, which operation places transformer 303 in the-standby-conditiom ,The on-off pilot lamp 306 glows as an indication that the main power supply is being received. Next, the remote control on-oif switch 3 I 2 is operated, whereby the associated contact 3I5 is closed to supply main A. C. to radio transmitter 30I, radio receiver 328, and transformers 327 and 329. The transmitter, the receiver, tone oscillator 389 and tone detector 393 at the radio station are thus placed in the standby condition.

Operation of on-ofi switch 3I2 is accomplished by the momentary operation of switch I50 at the telephone ofiice auxiliary equipment (Figure 1) so as to operate the left-hand contact spring sets of switch I50, or alternatively, by the momentary operation of switch 3I9 (Figure 3) at the radio station.

Mobile unit 500 is placed in the standby condition by the operation of master switch 538 (Figure 5), which operation connects battery potential to the circuits of the mobile unit.

Outgoing calls (telephone office to a mobile unit) On an out-going call from substation T of the telephone ofiflce to a mobile unit, the calling person dials the digit, or digits, of the mobile unit directory number necessary to select the radio channel terminals in the telephone oflice auxiliary equipment (Figure l) Line circuit 1 (Figure 1-A) operates in order to place battery potential upon control conductor 5, and ground potential upon start conductor 8 of distributor 9. Distributor 9 assigns an idle link, finder I0 and selector II for example, and finder I0 seizes line 2 in well-known manner. Line circuit'l places ground potential upon conductor 6 to mark line 2 as busy to the connectors, such as 22. Line circuit 1 releases distributor 9, and selector II is conditioned to receive the first dialed digit. Ground potential is connected to out line simplex conductor I10 and extended to the center tap of the lower winding of transformer I83, through both sections of this winding and armature springs I5I and I54 and associated resting contacts to out" line conductors I and I5 leading to the radio station.

At the radio station, the conductors pass through break contacts of jacks 205 and 206, lefthand windings of repeating coil 233, both windings of relay 2 I0, center tap of relay 2I0 to conductor 293 as a simplex, and conductor 293 through the winding of line relay 355 to battery, causing relay 355 to operate. Relay 2I0 does not operate over this circuit because its windings have simplex current flow which opposes magnetically. At armature 351, relay 355 completes an obvious circuit to relay 360, causing relay 339 to operate. At armature 355, relay 360 extends ground over conductor 302 to radio transmitter 30I for starting transmitter 30I in well-known manner. Armature 385 also completes an obvious circuit to transmitter start pilot lamp '301, causing pilot 301 to glow as an indication that the transmitter start circuit has been completed. Ground returned from transmitter 30I in wellknown manner over conductor 32'3'caus'es pilot lamp 308 to glow as an indication that the transmitter is actually on the air. w I

The ground potential returned from transmitter 30I over conductor 324 is extended to relay 220 (Figure 2) by way of armature 343 and conductor 298, causing relay' 220 to operate. At armatures 22I and 222 and associated Working contacts, relay 220 extends battery and ground respectively to the inner terminals of the left-hand windings of repeating coil 231, thereby to completea circuit through both windings of relay .aoaaiea.

H (Figure 1) over in line conductors I94 and I95 and the right-hand windings ofrepeating coil I93. A multiple circuit is also completed momentarily from the center tap of relay I'I0 through armature spring I56 and resting. contact of switch I50 to in line simplex conductor M3 to relay 0' (Figure 1-3) ofthe telephone oifice line equipment associated with this radio channel but relay H0 is of the slow-to-operate' type and, therefore, does not operate at this time. The windings of relay II0v (Figure 1) aid each other when serially connected in a loop circuit to thereby cause operation. of relay H0, and oppose each other when a parallel, or simplex, circuit is completed therethrough. Relay IIO, therefore,.operates at this time.

At armature III, relay II0 connects continuous ringing current through capacitor I24 to conductor I1I for extending a simulated dial tone back to the calling person to indicate that the desired radio channel has been seized and that the dialing of the desired mobile unit may now be accomplished. At armature I- I2, relay IIO completes an obvious multiple circuit to relays I and I30 through temperatureecontrolled resistors I25 and I35 respectively. Relays I20 and I cannot operate through the. normal high resistances of the associated resistors I25 and I35.

After a period of approximately five seconds, the resistance of resistor I25 is lowered sufliciently in well-known manner to permit relay I20 to cuit for itself, thus preventing recurrence of continuous ringing current to conductors III on this call. After another period. of approximately five seconds, the resistance of resistor I is lowered sufliciently in well-known manner to permit relay I30 to operate and lock to ground by way of armatures I32 and II2. At armature I31, relay I30 connects interrupted ringing current through capacitor I34, armature I2I and working contact, and armature III to conductor III for extending a simulated ring back tone to the calling person to advise the calling person that the desired mobile unit is being signalled. Since relay I30 is locked in the operated position, this simulated ring back tone will maintain until the mobile unit answers or until the call is abandoned. The abandonment of'the call releases relay 360 to cause radio transmitter 30I to be taken on the air and thereby cause the restoration of relay 220.

The calling person starts the second dialing (the last two digits of the wanted mobile units directory number) upon the receipt of the abovedescribed simulated dial tone, and the dialing of these two digits is usually completed before the delayed operations of relays I20 and I30 apply the simulated ring back tone by way of armatures I3I and I2I.

The "second dial impulses intermittently restore relay 355 in.- well-known manner, with relay 360 remaining operated during the impulsing period due to its sl-ow-to-release characteristic. The operation of relay 360 completed an energizing circuit for bias voltage-divider 325 by way of conductor 336. armature 3'46 and resting contact, and armature 363 and working contact; and, at armature 364 and working contact, extended 250-volt anode supply totone oscillator 389 by way of the upper left-hand winding of transformer 331, resistor 343, and right-hand plate of tube320. Oscillator 383. therefore. starts winding of transformer 331 respectively constituting the: feedback (tickler) and output windings. Resistor MiG-amt. capacitor 361' comprises the bypassed-grid-resi-stor combination for increasing negative gridbias. as a. function of? grid current (rectified: portibncof positive grid voltage loops in access ofnet grid bias-i. Resistor. 35 9 is a nonbypassed-resistor-r servmg to stabilize oscillator frequency by; increasing grid-circuit series :impedance and,.hence,;-reducing grid circuit loading on the tunedcircuit. Resistor 348: is a resistor. in the anode: circuit whichincrea's'e's the total impedance facing the ,upperIleit-hand (tickler) winding" of transformer 33? and. hence, reduces the loading on the: tunedzcircuit'to improve its Q and. thexresulting frequency stability.

.Re'tumin'gxnow'to .thezdescription of the call from'the telephone ofiice to the dialed mobile unit, reception 'oftheradio station's carrier from transmitter. 3'0I simultaneously by'the. radio receivers of all:.mobil'e unitsi-in'the standby condition operates theirelated squelch-relays, such as H0 in Figure 4; The tone impulses fromradio transmitter 30I are converted into multiple operations of the lineWelays, such as 545 in Fi ure 5, of the mobile rmits in the-standby condition, starting the train of impulse receiver operations to be described later; and culminating in either nonresponse'of the dialed mobile unit or in the appearance of the dialed mobile units carrier on the air should the dialed mobile unit answer the call. Should there be no answer to the call, the calling person will return the hand set to the cradle of the telephone, thereby causing the restoration of relays 355 and 360 to remove radio transmitter 30 I from the air and thus cause the restoration of relays 220, III), I20 and I30. Should the dialed mobile unit respond to the call, its radio transmitter carrier is received by receiver 328 (Figure 3) at the radio station thereby to applygroundpotential to conductor 36*8'in well-known manner. Ground potential on conductor 358' causes the operation of squelch relay 340 which completes a locking circuit for itself by way of armatures- MI and 362. Relay 340 is of the slow-to operate type in order to avoid possible operation on ignition or other transient interfering signals before the carrier from the radio transmitterof thedlaled mobile unit is removed'atrreceiver 320 of the radio station.

At armature346', relay 340 disconnects the250- volt. anode :supply from tone oscillator 389 to disable the oscillator; and, at armature 341, opens the output circuit of tone oscillator 389. At armature 343, relay 340 opens the circuit to relay 220, causing relay 220 to restore. At armatures HI and 222, relay 220 removes battery and ground from in" line conductors I94 and I95 thereby causing the restoration of relay I I0, and, at :armatures 22I and 222 andassoclated resting contacts, restcres.the.l'n line circuit-to its normal simplex supervisory condition, ground being extended by way of armatures 31I, 344, 2 and resting contact to the inner terminals or the lefthand winding of repeating coil 231. This simplex signal ispicked up at the center tap of relay IIO (Figure 1) and expended to "in line supervisory signal conductor I13 by way'of armature spring I56 and resting contact, from which point it is made available to the line circuit equipment in the telephone ofiice for use as an answering supervisory signal in a manner similar to that employed on a physical connection between two ordinary stations of the telephone exchange system. The restoration of relay IIII removes the interrupted ringing current from conductor "I at armature III and, at armature II2, opens the multiple locking circuits of relays I20 and I30 thereby restoring the timing arrangement to normal.

Relay IIII (Figure 1) does not operate in the simplex circuit over conductor I13 but relay (Figure i-A) does operate over the mentioned simplex circuit. At contact II3, relay 0' completes an obvious operating circuit for relay I50. At contact I52, relay I50 completes an operating circuit for relay I40 by way of contact I62, relay I60 having previously operated by way of contact 63. At contact I45, relay I40 completes a holding circuit for relay I60 by way of contact I61. At contact I44, relay I40 completes an operating circuit for reverse-battery relay 50 by way of contact II3. Relay 50, upon operating, reverses the battery polarity of the outgoing trunk in well-known manner, which reversal of polarity may be utilized for metering or supervisory purposes. tion is established from calling substation T over the automatic telephone exchange I, repeater 49, telephone office auxiliary equipment I19, radio station control circuit 300 to the called mobile unit 500. The outward talking circuit extends from substation T, over conductors 3-4, finder I0, selector II, conductors I4-I5, contacts 5I-53, 93-95, conductors Ill-I12, repeating coil I83, contacts of test switch I50, conductors l90-I9I, monitor jacks 205-206, repeating coil 236, conductors 290-29I to the audio frequency input of transmitter 30I, whereby the audio frequencies are impressed upon the carrier and transmitted to the radio receiver 400 in mobile unit 500, and whence they appear across the audio frequency output and thence over armature 423 and working contact and conductor 522 to the receiver of handset 50I. Speech impressed upon the transmitter of handset 50I is transmitted over conductor 412 to the audio frequency input of radio transmitter 40I, from whence it is superimposed upon the transmitter carrier. Radio receiver 328 located in radio station control circuit 300 receives the incoming modulated carrier and impresses the voice currents upon conductors 294- 295 (through the band pass filter 334)- which are connected to repeating coil 231, whereupon the voice signals are induced into the secondary of repeating coil 231 and extended over monitor jacks 203-204, conductors I94-I95, repeating coil I93, repeating coil I83 to conductors I1I- I12, and over conductors I1I-I12, contacts 93- 95, 5I-53, conductors I4-I5, selector II, finder I0, and conductors 3-4 to substation T. It should be understood that, during the conversation, the mobile unit's radio transmitter 40I is on the air only while the person at th mobile unit is speaking, and, is off the air while he is listening to the person at the calling station.

At this time a talking connec- 14 Squelch relay 340 is, therefore, locked to armature 362 of relay 360 on the first appearance of the mobile units carrier, in order that the control of the established connection is vested in the calling station or the telephone oflice.

Upon the termination of the conversation and the cradling oi the handset at the calling station, the circuit to relay 355 (radio station) is broken. causing relay 355 to restore. At armature 351, relay 355 opens the circuit to relay 360, causing relay 360 to restore. At armature 362, relay 360 opens the circuit to squelch relay 340, causing relay 340 to restore. At armatures 365 and 345 respectively, relays 360 and 340 disconnect multiple grounds from conductor 302, thereby causin the removal of the radio stations transmitter 30I from the air. At armature 344, squelch relay 340 disconnects the ground simplex from the inner terminals of repeating coil 23'! to complete the restoration of the system.

Referring now to Figures 4 and 5 disclosing the circuit details of one of the mobile units (500). a description of the operation of this equipment will now be given. As previously explained, the tone impulses from the radio station's transmitter 30I are converted into multiple operations of the line" relays, such as 545 in Figure 5, of all the mobile units in the standby condition. The pulsing is received from the radio station at mobileunit 500 as splashes" of tone modulation of the incoming transmitter carrier at approximately 3000 cycles. These tone splashes (one for each dial impulse) are rectified by the full-wave rectifier 4H, and the resulting direct current over conductors 523 and 524 operates relay 545 accordingly. Capacitor 429 is connected across the rectifier circuit to improve efiiciency, i. e., to remove the effect of the load (relay 545) inductance by removing the A. C. component. A compromise value of capacitor 429, rather than a higher value giving greatest rectification efiiciency, is desirable in order that relay 545 shall follow the pulse shape, and an appreciable improvement in rectification efficiency is accomplished while maintaining a good approximation to the original pulse ratio.

Assuming now that the mobile unit shown in Figures 4 and 5 is the unit dialed by the calling station of the telephone system, then the received tone impulses, appearing as operations of relay 545, control the impulse receiver circuits to identify the call for the related mobile unit and to signal the person at this mobile unit. It should be understood at this time that the appearance of the radio station transmitters carrier on the air upon the initiation of this call caused the operation of a squelch relay (not shown) in mobile unit radio receiver 460 which applied ground potential in well-known manner to conductor 409 leading to squelch relay 4| ii, thereby causing the operation of relay 4I0. Relay M0 is of the slow-to-operate type to avoid operating on interference.

The first pulse operation of relay 545 completes a circuit to relay 555 from ground, armatures M3, 424, conductor 52B, 511 and resting contact, conductor 509. armature 541, winding of relay 555 to battery, causing relay 555 to operate. Relay 555 is of the slow-to-release type and, therefore, does not restore during the first impulse series. At armature 551, relay 555 completes a circuit to pawl magnet 558 of minor switch 554 from ground on conductor 509. At armature 546. relay 545 completes an obvious circuit to motor magnet 559 of switch 554 for each impulse in the first series of impulses, and since relay 555 is holding pawl magnet 558 operated, motor magnet 559 drives wipers 566 and 561 in wellknown manner to the contacts in banks 564 and 565 corresponding to the digit dialed, which in this instance is assumed to be the digit 4.

Shortly after the cessation of this series of impulses, relay 555 restores and completes a circuit to relay 566 from ground on conductor 569, armatures 556, 562 and resting contact, wiper 566, contact 4 of bank 564, winding of relay 566 to battery. Relay 566 operates and locks to ground on conductor 569 by way of armature 563. At armature 562, relay 566 disconnects wiper 566 from conductor 569 and, at armature 562 and working contact, connects conductor 569 to relay 556. Relay 556 operates approximately 100 milliseconds later due to its sleeve and capacitor 553, and locks to conductor 569 by way of armature 55!.

The restoration of relay 555 also opens the circuit to pawl magnet 558 at armature 551, and pawl magnet 556 causes the return of wipers 556 and 561 to their home positions in well-known manner. The delayed operation of relay- 555 permits suificient time for wipers 565 and 561 to be returned to their home positions before armature 552 extends conductor 569 to wiper 561 by way of armatures 556 and 512. Thus there can be no false operation through bank 565 while wipers 566 and 561 are being returned.

At armature 546, relay 545 completes an obvious circuit to motor magnet 559 for each impulse in the second series of impulses, and since relay 555 operates on the first impulse to hold pawl magnet 558 operated, motor magnet 556 drives wipers 566 and 561 to the contacts in banks 564 and 565 corresponding to the digit dialed, which in this instance is assumed to be the digit 6. Shortly after the cessation of this series of impulses, relay 555 restores and completes a circuit to relay 516 from conductor 569, armatures 556, 552, 512, wiper 561, contact 6 of bank 565, winding of relay 516 to battery, causing relay 516 to operate; and, at armature 551, opens the circuit to pawl magnet 558 thereby to cause the returning of wipers 566 and 561 to their home positions in well-known manner. At armature 51!, relay 516 completes a locking circuit for itself to conductor 521: At armature 512, disconnects wiper 561 from conductor 566; and, at armature 513, completes the circuit for line buzzer 563 from ground, armatures M3, 424,.conductor 526, 513, winding of buzzer 5523, master switch 536 to battery, thereby advising the person in this mobile unit that he is being signalled from the telephone office. The audio output circuit from the right-hand winding of repeating coil 235 to the input circuit (not shown) of radio transmitter 36! is maintained at armature 356 and working contact upon the termination of the dialing by the calling station of the telephone office.

Responsive to the lifting of the handset from the cradle at the mobile unit inanswer to the call, relay 426 operates from ground, armature spring 566 of the handset cradle switch, armatures 55!, 514, conductor 529, winding of relay 426 to battery, and locks to ground at armature spring 566 by way of armatures 425 and 56! independent of relay 516. The lifting of the handset also causes the handset-off-cradle pilot 561 to glow over an obvious circuit to serve as a warning signal that the handset should be prcperl cradled at the terminationof the call;-

At armature 422', relay 426 starts the mobile units radio transmitter 46! as hereinafter explained; and, at armature 423, shifts the audio output circuit of radio receiver 466 from the pulse detector input to the receiver of handset 56! by way of conductor 522 and direct ground. The rectifier 4!1 receives considerable power (probably over 0ne-half watt) of tone from radio receiver 466, whereas the receiver of handset 56! requires only approximately 6 milliwatts. Attenuator 466 provides for this difference. At armature 424, relay 426- disconnects ground from conductor 569, thereby to restore relays 556 and 556 to conserve battery power from the battery of the mobile unit. The operation of armature 424 also opens the circuit of buzzer 566.

The person at the mobile unit then depresses the TL (talk-listen) button 5!8 in the handle of handset 56! to speak to the calling person, and permits button M8 to restore when he wishes to listen to the calling person. The depressing of TL button 5l8. operates the switch inside the handle of handset 56! thereby to shunt down the receiver of handset. 56!, and to connect ground to conductor 525v for causing the operation of TL relay 465 in transmitter 4610f the mobile unit. At armature 466, relay 465 disconnects the antenna wiring of receiver 466 from the antenna: at contact 461, grounds the antenna wiring of receiver 466; and, at armature 466 and working contact, connects the output circuit (not shown) of transmitter 46! to, the antenna thereby placing transmitter 46-! on the air. The output circuit from the transmitter of handset 56! may be traced from ground, transmitter, conductor 412, armature 43! and resting contact, to the output circuit (not shown) of transmitter 46-! over conductor 432, and back over conductor 463 through capacitor 463 to ground. The releasing of TL button 5!B opens the circuit of TL relay 465, permitting relay 465 to restore and (l) disconnect the output circuit (not shown) of transmitter 46! from the antenna, (2) disconnect ground from the antenna wiring of receiver 466, and (3) connect the antenna wiring of receiver 466 to the antenna thereby placing receiver 466 on the air.

squelch relay 4l6 at the called mobile unit was operated responsive to the carrier from transmitter 36! of the radio station being received at radio receiver 466 of the called mobile unit, for the purpose of looking out mobile unit 566 to prevent activation of radio transmitter 46! should the person at the mobile unit initiate a call at this time. The original operating circuit of relay 4!6, however, was destroyed when radio transmitter 46! was placed on the air responsive to the person at the called mobile unit lifting his handset 56! and pressing TL button 5!!! answer the call. The pressing of TL button 5l8 causes TL relay 465 to operate and switch radio transmitter 46! on the air. At the same time, however, TL relay 465 disables radio receiver 466. An. auxiliary operating circuit for relay M6 is,

therefore, established during the periods that the battery. Relay M6 is also of the slow-to-.rele ase type and, therefore. is held continuously'oper- 17 ated in the cycle wherein its first operating circuit is completed by radio receiver 400, then opened by the disabling of radio receiver 400. next, the auxiliary operating circuit completed by the operation of TL button 518, followed by the disabling of the auxiliary operating circuit responsive to the releasing of TL button 518 and the re-establishment of the first operating circuit as radio receiver 400 is switched back on the air.

Upon the termination of the conversation and the cradling of the handset at the calling station, transmitter 301 at the radio station is removed from the air in the manner previously explained, whereupon the squelch relay (not shown) in radio receiver 400 of the called mobile unit restores to remove ground from conductor 409. Responsive to the releasing of TL button 5I8 in handset 5!, the auxiliary operating circuit for relay M is opened, and relay 4|0 now restores. At armature 4I3, relay 410 disconnects ground from conductor 521 to cause the restoration of relay 510, thereby restoring the impulse receiver of the called mobile unit to normal. Responsive to the cradling of handset 50l at the mobile unit, the operation of armature spring 506 of the handset cradle disconnects ground from armature 425 of relay 420, thereby causing relay 420 to restore. At armature 422, relay 420 removes radio transmitter 40! from the air; and, at armature 423 and resting contact, returns the audio output circuit of radio receiver 400 to the pulse detector input circuit of rectifier M1. The system is now in the normal standbv po tion.

The starting of radio transmitter 40l of the mobile unit is accomplished in the following manner. Relay 420 is operated upon thelifting of handset 50l from the cradle and, at armature 422, completes the circuit to start relay 435, causing relay 435 to operate. At contactor 436, relay 435 extends battery through fuse 438 and resistor 434 to conductor 433 for supplying transmission battery to the transmitter of handset 50L At contactor 436, relay 435 also extends battery through fuse 439 to the primary side (6-volt) of dynamotor 431 thereby to cause dynamotor 431 to start and continue to run as long as handset 50! remains off the cradle. The secondary side of dynamotor 431 supplies the comparatively high anode voltage for radio transmitter 401 in well-known manner. Fuse 439 is a heavy current fuse designed to withstand the momentary large starting current of dynamotor 431, and also to afford protection against short circuits and other defects resulting in continuing current in excess of the continuous carrying capacity rating of the fuse.

Considering now the case when the mobile unit shown in Figures 4 and is not the unit indicated by the first dialed digit from the calling station in the telephone system, then the first pulse operation of relay 545 completes a circuit to relay 555 from ground, armatures M3, 424, conductor 528, 511, and resting contact, 541, winding of relay 555 to battery, causing relay 555 to operate. Relay 555 is of the slow-to-release type and, therefore, does not restore during the first impulse series. At armature 551, relay 555 completes a circuit to pawl magnet 558 from ground on conductor 509. At armature 546, relay 545 completes an obvious circuit to motor magnet 559 for each impulse in the first series of im pulses, and since relay 555 is holding pawl mag- 566 and 561 in well-known manner'to the contacts in banks 564 and 565 corresponding to the digit dialed, which in this instance is assumed to be the digit 3.

Shortly after the cessation of this series of impulses, relay 555 restores and completes a circuit to relay 515 from ground on conductor 509, armatures 556, 562 and resting contact, wiper 566, contact 3 of bank 564, multiple wiring from contact 3 of bank 564 to contact l0, winding of relay 515 to battery, causing relay 515 to operate. Relay 515 completes a locking circuit for itself through armature 511 and working contact. At armature 516, relay 515 disables the impulse detector circuit and, at armature 511, disables the impulse receiver-circuit to stop all further response. At armature 518, relay 510 completes the circuit of busy" lamp pilot 5I9, causing pilot 519 to glow as an indication that the radio system is in use. Should handset 50| be lifted from the cradle while busypilot 519. is glowing, a circuit is completed through armature spring 505 of the handset cradle switch to buzzer 508 from ground, armature 518, armature spring 505, buzzer 508, master switch 5l8 to battery, causing buzzer 508 to sound as an audible signal that the radio system is in use. The person at this mobile unit, however, cannot break into the circuit since the lifting of handset 50l cannot cause the operation of relay 420 (which is transmitter 40l control) because armature 514 of relay 510 is in .the unoperated, or open, position and armature 4l4 of relay 4) .is in the operated, or-open, position.

Considering now the case when the mobile unit shown in Figures 4 and 5 is a unit indicated by the first dialed digit 4 from the calling station in the telephone system but is not the unit indicated by the second dialed digit (3, for example) from the calling station, then upon receipt of the first digit (4) relays 560 and 550 are operated and locked, and wipers 566 and 561 are returned to the normal position in the manner previously explained for the digit 4. At armature 546, .relay 545 completes an obvious circuit to motor magnet 559 for each impulseof the second digit 3, and since relay 555 .operates on the first impulse to hold pawl magnet 558 operated, motor-magnet 559 drives wipers 566 and 561 to the respective third contacts in banks 564 and 565. Shortly after the cessation of this series of impulses, relay 555 restores and completes a circuit to relay 515 from ground on conductor 509, armatures 556, 552, 512, wiper 561, contact 3 of bank 565, multiple wiring from contact 3 of bank 565 to contact l0, winding of relay 515 to battery, causing relay 515 to operate. From this point on, the functions of relay 515 are the same as described in. the preceding paragraph.

Incoming calls (mobile unit to' telephone ofl'ice) On an incoming call to the telephone omce from a mobile unit, the person at the calling mobile unit (Figures 4 and 5, for example) first observes that radio circuit busy lamp pilot 5l9 is not glowing, and then removes handset 50l from the cradle. Lifting handset 50l causes ground to be connected to armature spring 506 of the handset cradle switch thereby to operate relay 420 by way of armature 59l, conductor 530, 414, winding of relay 420 to battery. Relay 420 locks to the ground on armature spring 506 b way of armatures 425 and 591.

At armature 42I, relay 420 completes a circuit to the filament of tube 404 in tone oscillator 489 1.9 to provide quick heating and thusreducestandlby power requirements. At armature 422, relay 420 starts radio transmitter 401 in the. man-.- ner previously described in the section. titled Outgoing Calls (Telephone Ofilce. To A.Mobile Unit). At armature 423, relay 420 transfers the audio output of radio receiver 400 from the pulse detector input to the receiver of handset 50I, in anticipationofdial tone from the telephone ofiice. At armature 426, relay 420 completes a circuitv to TL relay 405 in radio. receiver I from ground, armatures 426,.4I5, resistor 402, winding of TL relay 405 to battery, causing relay 405 to operate and place radio transmitter 40I on the. air in. the manner previously described in.-the:section titled Outgoing Calls. (Telephone Oflice'll'o A .Mobile.Unit)..

The-placing of; radio transmitter. 401. on. the air causes. its. carrier. to be. received by radio receiver. 320.at. theradio. station. (provided that the.mobile. unit .is patent of. range) and'transmitter 30I at..the..radio station is.immediately startedand placed.on. theair. in the following described manner.. Groundpotential applied to conductor 368 by radio receiver 328 in well.- known. manner causes the operation of squelch relay 340 which completes a locking circuit for itself by way of armature MI and the grounded armature spring 3220f timer 32I. At armature 345, relay 340 extends ground over conductor 302 to radio. transmitter 31H 'for starting transmitter 30] in well-known manner. Armature 345a1so completes an obvious circuit" to transmitter start pilot lamp 301, causing pilot" 301 to glow as an indication that the transmitter start circuit. has. been completed. Ground returnedlfrom transmitter 30I in well-known manner over conductor 323 causes pilot lamp 308 to glow as an indication that transmitter 30I is actually on. the air.

At. armature 3'42, relay 340'closes the motor circuit of timer 32I, causing timer 32I to onerate and, after the expiration of a predetermined" time interval, disconnect the ground spring from armaturespring 322,'thereby'opening the locking circuit of. relay 340. This timed interval is of sufficient duration topermit dialling by" the calling person in the mobile unit and answer by the called telephone station under average conditions. If, however, the called telephone station does not respond before the timed interval lapses, timer 32I' then opens the locking circuit of' relay 340 thereby to restore the. radio station control circuit 300 for general.use,.unless thecalling person maintains relay 340 operated by the pressingof. the. TL button 518 in his handset.

Timer 32I may be of. any conventional type which opens its contact after a predetermined timed interval and capable of continued stalling 'after'iti reaches the end of the timed interval on. a

call where conversation proceeds. It also restores quickly to normal position upon the release of relay 340', in order to be prepared for a call immediately following the present call.

At armature. 344, relay 340 extends ground by. way of armatures 3', 344, 2H and resting contact to the inner terminals of the left-hand Winding of repeating coil 231. This simplex signal is. picked up at the center tap of relay I I (Figure I) and extended to in line supervisory signal. conductor I13 by way of armature spring I56 and resting contact, .from which point. it is made available to the line circuit equipment in.the telephone oflice for seizing. a

connecting link. Relay IIO (Figure. 1)., however, does not operate. over the mentioned simplex circuitbut relay IIO' (Figure 1-3) does operate over the simplex circuit. At contact H3, relay IIO completes an obvious operating circuit to relay I50. At contact I5I, relay I50 completes an operating circuit to relay by way of contact I SI and the upper. winding of relay 90.

At contacts 93 and 95, relay 90 interrupts the normalconnections betweenconductors III-I I2 extending from coil.I83. of telephone office auxiliary equipment I19 and line conductors I I-I5 extending to selector II in the automatic exchange I. At contacts .9I, 92and-94, relay 90 completes a connection between. conductors I 'I I-I 12. extending from coil. I83-andline-conductors I'I-I8.extending toselector24. At-contactel, relay 90 connects. the. upper. winding. of. relay I00.- across line conductors I-1-I8 to. eifect seizure of selector 2.4. At. contact. 91, relay 90 disconnects battery potential from conductor I6. and, at contact 96,.connects. ground potential tocontrolconductor. IS. The normal marking of outgoing trunk. It as idle is thusremoved, and outgoingtrunk I2 is now marked as busy to the outgoing selectors.

When incoming selector 24 is seized by repeater 49- as noted above, ground potential .is returned by the selector over conductor I9 to energize the lower windings of relays 90 and I00inmultiple. Relay I00 does not operate at this time since. it is of the shunt-field type and will not operate until-both its windings-areenergized in such directions: astoproduce the. same magnetic polarity.

At armature 346. and working contact, relay 3.40 extends 250-volt. anode supply over conductor-3'36 through armature 3-64 and resting contact? to bleeder 325. andalso through. armature 364 and resting contact, armature 363 and resting contact, winding of relay 370 to. the left-hand-plate of tube 320, thus preparing-tonedetector. 393 for reception of the dialing from the calling mobile unit.. The bleeder 325- provides. the necessary near-cutoff bias for plate rectifier action of :tone detector 393.to operate relay 310 on. every tone pulse received.

At armature 341 and working contact, relay 340 completes the audio output circuit from the right-hand winding of repeating coil 236 to the input circuit. (not shown) of radio transmitter 3IlI As. previously explained, -the operation. of relay 90 connects. the. upper winding, of relay I00 at. contact 9.I acrosslineconductors I] and. I8 leading to. incoming selector. 24. Dial tone. is thereby impressed uponrepeatingcoil 23$.from battery through the upper winding of line relay 35; contact 3| of switchingrthrough relay 30,.line conductor. I'I, contacts 9|, '92, conductor III, repeating coils I14, I83, conductor I11, armature I5I and resting contact, cut-01f jacks 205, 206 and from ground, upper winding of transformer 31 (transformer 31 being activated throughits lower winding from dial tone source 38) resting contact of overflow sprin contact set 36, lower winding of line relay 35, contact 32 of switchingthrough relay 30; line conductor I 8, contacts I I I, 94', conductor I72, repeating coils I14, I83, conductor I18, armature I54and resting. contact, and cut-off jacks 205, 206. Dial tone is, therefore, repeated over the audio circuit through radio transmitter 30I, over the radio link to the input circuit (not shown) of radio receiver 400at' the calling mobile unit in well-known manner, and

21 from the output circuit (not shown) of radio receiver 400 to the receiver of handset 50I over conductor 522 and ground. The person at the calling mobile unit is thus advised that the dialling of the wanted .telephone station of the telephone ofllce may now be accomplished. Patent No. 1,841,679 discloses and describes a, selector having the typical dial tone circuit shown in Figure 1-A of the present invention. The person at the calling mobile unit then dials the number of the wanted telephone oflice station.

The transmitter carrier of the calling mobile unit is put on the air by the lifting of handset 50I when initiating the call, and is automatically taken or! the air after approximately two seconds, during which time the carrier has served the purpose of causing the transmitter carrier of the radio station to come on the air in acknowledgement, providing that the calling mobile unit is not out of range. The automatic removal of the carrier from radio transmitter 40I is accombattery of the mobile unit have its "positive" con-' nected to the metal frame of the chassis.

The impulses from contact 5 I 2 of dial 5 I 0 cause pulse operations of relay 430 over conductor 414;

and relay 430 correspondingly operates armature 43I. The operations of armature 43I disconnect the input circuit (partly shown) of radio transmitter 40I from its normal connection to the transmitter of handset 60I by way of conductor 412, and transfers this input circuit across resistor 446. Relay 430, therefore, applies the dialed impulses in the form of tone "splashes" to the radio modulation circuit (not shown) of transmitter 40I from which they are transmitted as modulations on the outgoing carrier, transmitter 40I being placed on the air at the beginning of each digit dialing by TL relay 405 operating from ground through contact 442. Control circuit 300 at the radio station relays these tone splashes to plished in'the following manner. Resistor 402 is in series with the winding of the relay 405, and

responsive'to the completing of the circuit to relay 405 byway of armatures 426 and H5, temperature-controlled resistor M8 is connected across the winding of relay 405 through armature 4 I 2. The relatively normal high resistance of resistor 4I8 permits relay 405 to operate. Within approximately two seconds, the resistance of resistor M8 is lowered sufficiently to shunt out relay 405, and relay 405 thereupon restores. Theknown manner. The operation of relay 4I0 and its functions are described in the section titled Outgoing Calls (Telephone Office To A Mobile Unit).

As each digit of the wanted telephone number is dialed at the calling mobile unit, oil-normal contact 5I3 of dial 5I0 operates relay 440 over an obvious circuit. At armature 44l, relay '440 extends high voltage supply from radio receiver 400 to the plate of tube 404 by way of resistor 445 and the upper left-hand winding of transformer 4I9. Since the prior operation of relay 420 completed the filament circuit of tube '404 at armature 42I. tone oscillator 483 starts-to function, and approximately 3000-cycle voltage appears across resistor 446 which is the stabilizing load.

Tone oscillator 480 is conventional, of the tickler type with feed back and loading coupling held to a minimum, and the bypassed resistor 466 and non-bypassed resistor 459 combination provided to reduce the effect of the grid as a load on the tuned circuit, all for the purpose of improving frequency stability. Bias for the tube 404 is a combination of the drop across resistor 466 (due to grid current) and the drop across the series filament resistor 441. This method of obtaining a grid bias, partially from grid current and partially from the fixed source. provides increased stability because of the lesser grid circuit loading on the tuned circuit while retaining sufficient of the self-compensating characteristics of grid-current bias to satisfy circuit requirements against variations in supply voltage, etc., it does, however, require that the the telephone oiflce equipment in the following described manner.

The dialed tone splashes are received over radio' receiver 328 and applied through armature 36I and resting contact, left-hand (coupling) winding of transformer 363 to the tuned circuit consisting of the right-hand winding of transformer 369 and capacitor 312. Plate rectifier action by tone detector 303, with bias obtained from voltage divider 325 activated by armature 346 and working contact through armature 364 and resting contact. and anode activated by armature 346 and working contact through armatures 364, 363 and associated resting contacts, and the winding of relay 310, results in one operation of relay 310 for each incoming tone splash corresponding to a dialed impulse. At armature 31I, relay 310 correspondingly interrupts the in line simplex signal circuit leading to "in line simplex signal conductor I13 and therefrom to the link in the telephone ofiice for switch-train control. Relay I I0 (lfigure 1-B) accordingly restores and re-operates over the inward simplex circuit at each received impulse, to control incoming selector 24.

At contact 3', relay IIO interrupts the circuit of relay I50 momentarily, but relay I50 remains operated as it is of the slow-to-release type. Each time relay I I0 restores and re-operates, it closes and then interrupts, at contact II2, a circuit to relay I30. Relay I30 operates upon the first closure, and remains operated during the succeeding interruptions in its circuit. At contact I3I', relay I30 completes a shunt path including resistor I16 in multiple with the upper winding of relay I00, thereby to improve the impulsing circuit of incoming selector 24. Also each time relay 0' restores and re-operates, it interrupts and then re-completes, at contact III, the loop circuit of incoming selector 24 to cause corre sponding operation of incoming selector 24 in well-known manner.

More particularly, incoming selector 24 operates in response to the first dialed digit to select an idle connector, such as 22, whereby connector 22 is conditioned to be responsive to the second and third dialed digits. At the conclusion of the first dialed digit, relay I I0, in its operated position, re-establishes the circuit of relay I 50' at contact I I3, and the loop circuit across line conductors I1I8 at contact III. Operated relay 0' also maintains interrupted, at contact N2, the circuit of relay I30. At contact I3 I, relay I30 opens the previously traced shunt path across the upper winding of relay I00.

The second and third dialed digits at the calling mobile unit correspondingly pulse the pre- 23 viously described simplex circuit which controls relay H (Figure 1-13), and relay H0 controls connector 22 to select the called station in the automatic exchange, for example, substation '1, in well-known manner.

Conventional ringing tone, if the dialed telephone station is not in prior use, or conventional, busy tone if the dialed telephone station is in prior use, is now received by the calling person of the mobile unit. Assuming that ringing tone is received and that the dialed telephone station answers the call, then relays 355 and 360 are operated in the manner described in the section titled OutgoingCalls (Telephone Oifice To A Mobile Unit). At armature 364, relay 360 disables tone detector 393 to: prevent possible faulty opera tion on open. circuit 00nd itions obtaining from the opening of the tone splash circuit to transformer- 359 at armature 36 and the closing of the output oi radio receiver 328 through to the in line circuit at armature 36l and working contact. At armature 3B2, relay 360 takesover control of the locking circuit of relay 340; and, at armature 365-, extends a multiple ground to conductor 362 for maintaining the starting circuit of radio transmitter 30L Conversation between the calling person at themobile unit and the called station of the telephone oflice now takes place, with the person at the called station talking and listening in the usual telephone manner, and the calling person at the mobile unit pressing TL button SIB while speakin'g'and releasing TL; button l8 while listening.

Upon the termination of the conversation and the cradling of the handset at the called telephone station, relays 355 and 360 are restored to normaL At armature 362, relay 36!! opens thelocking circuit to relay 348, causing relay 340 to restore. At armature 3'6l, relay 34!) transfers the input of radio receiver 323 from the in line circuit to tone detector 393. At armatures 365 and 345, relays are and 340 remove multiple grounds from conductor 302 thereby to disable radio transmitter The removal of the car-- rier of transmitter 39! from the air permits the restoring of squelch relay 4I0 at the calling mobile unit, and the cradling of handset at the calling mobile unit opens the locking circuit to relay 420 thereby to complete the restoration of the circuits and equipment of the mobile unit to the normal standby condition.

Should the dialed telephone fail to answer the call, the calling person at the mobile unit will abandon the call by returning handset 5M to thecradle.. The lapsing of the timed interval (timer 32-|)- opens the locking circuit of squelch relay 349 at armature spring 322, excepting should the calling person press TL button 518 and hold it depressed beyond thetimed interval in which.

case the presence of the carrier of radio transmitter 4M on the air retains relay 340 operateduntil TL button 5I8 is released. In either event, the restoration of relay 340 opens the in simplex signal circuit at armature 344: disables tone detector 393 at armature 346; and disables radio transmitter 30| at armature 345. The control circuit 300 at the radio station is thus returned to the normal standby condition, and the cradling of handset 50! at the mobile unit returns the circuits and equipment of the mobile unit to the normal standby condition as herebefore described.

The opening ofcontact 344 removes ground potential from the simplex circuit controllingre lay H0 (Figure 1-3), and relay H0 accordingly restores. At contact Ill, relay H0 opens the loop circuit to connector 22 thereby to cause the: restoration of connector 22 and line circuit 1. The restoration of connector 22 removes ground potential from the control conductor of trunk 2| which brings about the restoration of selector 2'4 and the removal of ground potential from con ductor IQ of incoming trunk 20.

The removal of ground potential from conductor l9 opens the multiple circuit to the lower windings of relays 90 and I00. At contact 3', relay I l 3 opens the circuit of relay I50, causing relay I50 to restore after a short interval. At contact I51, relay I50 opens the circuit to the upper winding of relay 90, and relay 90' accord ingly restores. At contacts SI, 92 and 94, relay 98 opens points in the circuit between outgoing. conductors. Ill-112 and line conductors ll-l8 and, at contacts 93-85 recompletes the circuit between outgoing conductors ill-I12 and: line conductors l4-I 5. At contact 96, relay'90 removes: busy ground potentiarrrom. control conductor It and, at contact 91, extends battery potential from impedance 10 to control conductor l6 thereby to mark outgoing trunk l2 as idle in the banksof selector ll.

Out-of-rangle signal On the initiation of an incoming call to" the telephone office from a mobile unit, the person at the calling mobile unit (Figures 4 and 5, for ex-' ample) causes relay 420 to operate and lock in the manner described in the first paragraph of the section titled Incoming calls (mobile unit totelephone ofiice). At armature 421, relay 420 completes an obvious circuit to buzzer 444 throughtemperature-controlledresistor 428 whereby buzzer 444 cannot operate until the resistance of resistor 428 is sufficiently lowered. Buzzer 444 is connected in series with the center leg of attenuator 408 and ground so that when resistor 428 heats sufiiciently to lower its resistance value sufficiently. buzzer 444 can operate.

In. approximately 5 seconds, the resistance. of resistor 428 is lowered sufficiently to permit buzzer 444 to sound as an out-of-range signal, providing that the carrier of radio station transmitter 30! has not been received by radio receiver 400 of the mobile unit within the 5-second period to cause squelch relay 410 to operate and open the circuit to buzzer 444 at armature M6. The person at the calling mobile unit, upon hear-- ing this out-of-range signal, will. restore handset 5BI to the cradle and move the mobile unit along several hundred feet or so when the average dead spot will have been passed. Another attempt at this point will ordinarily be successful.

The ,TL relay 405 control offered by resistor 4 I 8 and armature 412 of squelch relay 4!!! for initial onethe-air control, serves also as an out-o1'- range cut-on since it retains TL relay 405 in the normal position (not operated) if the radio station carrier is not returned by transmitter 30!.

Call timing In caseof an accident to a mobile unit, the handset (such as 50!) may be knocked oil? the cradle and remainin that unc'radled position for v cidently uncradled' without being noted during- 25 normal operation of the mobile unit. A partial guard against the latter condition is offered by thehandset-off-cradle pilot lamp 501 but this signal is a visual but not an audible one, and may be possibly overlooked for a time. For these reasons, and also to enforce a time limit on all calls, call timing facilities are provided.

When a two-way connection between a mobile unit and a station of the telephone oflice is first established, as evidenced by the operations of relays 420 and 4 I 0, the ground obtained from buzzer 444 on armature 6 of relay M is transferred by the working contact associated with armature M6 to the winding of relay 580 by way of conductor 52I, temperature-controlled resistor 520, armature 592 and resting contact and armature 582 and resting contact. Relay 580 cannot operate over this circuit until the resistance of resistor 520 is lowered sufliciently by heating which occurs in approximately two minutes,

whereupon relay 580 operates and locks to ground on armature spring 506 of the handset cradle switch by way of armature 582 and working contact, and armature 593 and resting contact.

At armature 583, relay 580 extends ground on conductor 52: to the winding of, relay 590 by way of temperature-controlled resistor 532 and armature 594 and resting contact. Relay 590 operates in approximately 1.5 minutes and locks to ground on armature spring 506 by wayof armature 594 and working contact. At armature 593 and working contact, relay 590 transfers the locking circuit of relay 580 to ground on armature spring 506 by way of resistor 533 and temperature-controlled resistor 534, but relay 580 cannot hold through the cold (high) resistance of resistor 534 and therefore, restores.

At armature 582 and resting contact, relay 580' connects it winding to ground on armature spring 505 by way of armature 592 and working contact and temperature-controlled resistor 534. The resistance of resistor 534 is lowered sufflciently in approximately 1.5 minutes to permit relay 580 to re-operate and lock to ground on armature spring 506 by way of armature 582 and working contact,

armature 593 and working contact, and resistors.

533 and 534. A total time of approximately minutes has now elapsed before relays 580 and 590 are in the operated and locked positions at the same time.

The locking circuit of relay 420 is now open at both armatures 58I and 59I, and relay 420 restores after an interval. At armatures 42I and 422, relay 420 disables the radio link connection; and, at armature 423 and resting contact, switches the output of radio receiver 400 to the incoming tone detector circuit. At armatures 584 and 595, relays 580 and 590 extend battery to buzzer 444 by way of temperature-controlled resistor 593, resistor 59'! and conductor 53I. Resistor 596 heats sufflciently in approximately three seconds to permit buzzer 444 to sound as a signal that the connection between the mobilev unit and the telephone office has been broken down as a result of the expiration of the time limit (approximately 5 minutes in the ideal case) Returning handset 50I to the cradle opens the locking circuit to relays 580 and 590, causing these two relays to restore. The circuit of mobile unit 500 is nowin the normal standby condition.

There are two reasons for obtaining the total 5 minutes timing period from three separate timing intervals. The primary reason is to allow for immediate recycling (i. e., another call immedi ately initiated or answered after a timing circuit has functioned wholly or partly on a preceding call) and, since the temperature-controlled resistors take about as long, or longer, to cool to ambient air as they do to heat, it appears obvious that the more the division of the total time the more equally will the full timing period be repeated on recycling, as the resistor used in the first division will have a greater proportional time to cool before it is re-used on an immediate recycling. The division into three parts, as shown, may possibly result in as much as two minutes deducted from the ideal 5 minutes for recycling, assuming the worst condition in which the preceding call was terminated at the end of the first two-minute interval, but the chances are that the combination of necessary elapsed time in immediate initiation of a new call and the fact that a preceding call will seldom be terminated at this most unfavorable moment, will considerably reduce the possibility of lessened timed intervals.

In the timing circuit operation just explained, there is a moment after the operation of relay 590 and before relay 580 first restores when both relays 580 and 590 are in the operated position simultaneously. Since simultaneous operation of these two relays is the ultimate method of designating the elapse of the full 5-minute timing interval by opening armatures 58I and 59I simultaneously and thus unlocking relay 420, relay 420 is made slow-to-release to avoid restoring on this momentary simultaneous operated positions of relays 580 and 590. The same simultaneous operation introduces the requirement for temperature-- controlled resistor 596 in thecircuitrof buzzer 444 to prevent buzzer 444 sounding prematurely..

Operating on-off ratchet switch 312 in radio control station Maintenance personnel in control of the telephone oflice auxiliary equipment (Figure 1) have a facility for operating on-oif ratchet switch 3 I 2 (Figure 3) located in the radio control station, thereby to turn the radio station control circuit 300 on or off, as the case may be. This facility in-' cludes key switch I50, associated out busy pilot lamp I I5, and associated in busy pilot lamp II1.

Since the radio station control circuit 300 may be m the on" position and a call in progress over control circuit 300 at a time when a maintenance.

man at the telephone office auxiliary equipment wishes to operate ratchet switch 3I2 in the radio control station, means is provided for enabling,

he manipulates switch I50 to operate the righthand spring sets of switch I50. Under this condition, should control circuit 300 be in use there will be ground potential on either out line simplex conductor I10 or on in line simplex conductor I I3, or both conductors. Ground on out line simplex conductor I10 will be extended to out busy pilot lamp II5 through armature spring II4-of switch I 50, thereby to cause pilot lamp II5 to glow. Ground on in line simplex conductor II3 will be extended to in busy pilot lamp I I! by way of armature springs I56 and H6, thereby to cause pilot lamp II! to glow. Should control circuit 300 be entirely free, the maintenance man will receive no signal from pilot lamps I I5 and III, since the negative battery po- 27 tential connected to the two simplex conductors through armature springs H4 and H6 will'meet negative battery potential already on the two simplex conductors, and the respective pilot lamps I I5 and I I1 will not find the necessary net voltage (diiference between telephone office and radio control station batteries) for illumination.

Assuming further that the preliminary test just described indicates that control circui 300 is not in use, then switch I50 is manipulated to operate the left-hand spring sets of switch I50. The out line is opened at armature springs I5I and I54, ground is connected to out" line conducor I90 by way of armature spring I5I and working contact, and battery is connected to "out line conductor I9I by way of resistor I05 and armature spring I54 and working contact, thereby to operate-relay 2 I in the radio control station over a loop circuit through its two windings. At armature 2 I 2, relay 2| 0 causes the operation of ratchet switch 3I2, thereby to turn control circuit 300 Oil at contact 3I5. Both manipulations of switch I50 are non-locking and, therefore, switch I50 is restored to normal position upon the removal of pressure. Ratchet switch 3I2 includes motor magnet .3I I, associated ratchet and cam wheels 3I3 3I4 and contact 3I5. It is remotely controlled over conductor 292 by the manipulation of switch I50 (Figure 1), alternate operations of contact 3| 5 turning control circuit 300 off or on as the case may be.

At armature 2H and working contact, the operation of relay 2I0 switches the in simplex conductor from the resting contact of armature 222 to the 48-volt supply in the radio control station by way of resistor 334. Pilot lamp I09 at the telephone ofiice auxiliary equipment'is connected to in simplex conductor II3 by way of armature spring I56 and working contact when switch I50 ismanipulated to operate the left-hand spring sets, and pilot lamp I09 will glow from the 48-volt supply in the radio control station, providing that control circuit 300 is in the on condition. If the operation of ratchet switch 3I2 is the alternate one which turns control circuit ofi, the 48-volt supply in the radio control station will also be turned off, and pilot lamp I09 will glow momentarily and then become dark.

Having described the invention, what is considered new and is desired to have protected by Letters Patent is set forth in the following claims: 1. In a radio telephone system for completing calls over antennae between stations connected to an automatic exchange and stations having radio transmitters and receivers, a radio control station connected to said exchange andhaving a radio transmitter, means responsive to the initiation of a call at one of said stations equipped with a radio transmitter and a radio receiver for activating said transmitter of said one calling station thereby to cause said transmitter of said calling station to place a radio frequency carrier on one of said antennae, means responsive to the placing of said carrier on said one antenna for establishing a communication channel to said control station and said exchange, means also responsive to the placing of said carrier on said one antenna for causing said control station transmitter to place its radio frequency carrier on another of said antennae, time-controlled means in said calling station for automatically disabling said transmitter of said calling station after a short timed interval, a dial tone source in said exchange, means responsive to the plac ing of said carrier of saidcontrol station transmitter on said other antenna for returning dial tone from said dial tone'source over said channel to said calling station, and means controlled by the transmitting of impulses corresponding to the number of a station connected to said exchange from said calling station for re-activating said transmitter of said calling station, thereby to re-establish said carrier of said calling station on said one antenna.

2. The telephone system claimed in claim 1, including means in all said stations equipped with radio receivers and transmitters, except said calling station, operated responsive to said carrier of said control station transmitter being placed on said other antenna for locking out all'sald stationsequipped with radio transmitters-and receivers except said calling station.

3. In a radio telephone system-as ciaimed m claim 1 wherein said last means includesa dial having a contact which is closed only duringthe pulsing periods of said dial, thereby 'to cause reestablishing of said carrier of said calling station on said; one antenna only duringthe-periodssaid dial is transmitting impulses.

4. The radio telephone system claimed in claim 1 together with time-controlled means in said control station, means responsivetosaid placing of said first carrier on said one antenna for operating said last time-controlled means, and means responsive to said lastoperated time-controlled means completing its'timed operation'for causing the removal of said second carrier from said other-antenna.

5. In a radio telephone system, a subscriber station having a radio receiver, a tone-rectifier connected to said radio receiver,-a pulsing relay connected to said rectifier, a signal, a stepping switch having two wipers, bank contacts accessible to. said wipers, a signal for said station, said pulsing relay operated intermittently responsive to a received series of tone pulses over said radio receiver and rectified by said rectifier for causing said switch to step said-wipers to bank-contacts corresponding to said received series of pulses, a wiper control relay operated responsive to one of said wipers connecting with one of said corresponding bank contacts for disabling'said one wiper, means for restoring said stepped wipers to normal'position and for partly preparing a circuit to said other wiper, a slow-to-operate relay operated shortly after said restoration of said wipers responsive to said operation of said wiper control relayfor completing said circuit to said other wiper, said pulsing relay operated intermittently responsive to a second series-of pulses from said rectifier for causing saidswitch to step said restored wipers to'other bank contacts corresponding to said second series of pulses, a signal relay operated over said completed circuit responsive to said other wiper connecting with one of said other bank contacts, and means responsive to said operation of said signal relay for operating said signal.

6. In a radio telephone system as claimed in claim 5 wherein said restoring means restores said re-operated wipers shortly after said operation of said signal relay.

7. In a radio telephone system, a station having an antenna, a radio transmitter normally disconnected from said antenna, a radio receiver normally connected to said antenna, and a slowto-release relay, means responsive to a radio frequency carrier received over said antenna by said receiver for completing a first circuit to said relay to operate said relay, meansresponsive to said 29: operation of said relay for seizing said station, means responsive to modulations of the radio frequency carrier received over said antenna by said receiver for signalling said station, means responsive to said station answering said signalling for switching said antenna from said receiver to said transmitter, said receiver disabled responsive to said switching of said antenna, said first circuit disabled responsive to said disablement of said receiver, means responsive to said station answering said signalling for completing a second circuit to said relay before said relay can restore in response to said disablement of said first circuit thereby to maintain said relay operated, said continued operation of said relay maintaining said seizure of said station.

8. In a radio telephone system for completing calls between stations over antennae, two stations each having time-controlled means and a radio transmitter, the time-controlled means of one of said stations having a shorter timing interval than the time-controlled means of said other station, means responsive to the initiation of a call at said one station for activating said transmitter of said one station thereby to cause said transmitter of said one station to place a radio frequency carrier on one of said antennae, means responsive to said initiation of said call for activating said time-controlled means of said one station, means responsive to said placing of said carrier on said one antenna for causing said transmitter of said other station to place a radio frequency carrier on another of said antennae, means responsive to said placing of said first mentioned carrier on said one antenna for activating said time-controlled means of said other station, means responsive to the completion of said shorter timing interval of said timed-controlled means of said one station for disabling said transmitter of said one station to remove said first mentioned carrier from said one antenna, and means responsive to the completion of said longer timing interval of said time-controlled means of said other station for disabling said transmitter of said other station to remove said second mentioned carrier from said other antenna after said disablement of said transmitter of said one station.

9. In a radio telephone system including fixed dial-equipped subscriber stations having lines terminating in an automatic telephone exchangeand other dial-equipped subscriber stations, a radio control station having a source of power, an outward talking circuit and an inward talking circuit connecting said exchange with said radio control station, means including radio communication facilities responsive to dial impulses for automatically completing calls between said fixed stations and said other stations over said outgoing and incoming talking circuits and said radio control station, means including two switches at said control station operated for serially extending said source of power to said radio communication facilities at said radio control station, thereby to enable said radio communication facilities, two indicating means at said exchange, means at said exchange operated for connecting one of said indicating means to said outward talking circuit and said other indicating means to said inward talking circuit, means including said outward talking circuit for activating said one connected indicating means should a call be in progress over said outward talkingcircuit, means including said inward talking circuit for activating said other connected indicating means should a call be in a progress over said inward talking circuit, and means at said exchange operated at a time when neither of said two indicating means are activated for operating one of said switches to disconnect said source of power from said radio communicating facilities, thereby to disable said radio communication facilities.

10. Ina radio telephone system having antennae for completing calls between stations connected to an automatic telephone exchange and other dial-equipped stations, a radio control station having a radio transmitter connected to one of said antennae, and a relay, means responsive to the initiation of a call by one of said connected stations for causing said control station transmitter to operate and place a radio frequency carrier on said one antenna, means responsive to said carrier being placed on said one antenna for operating said relay, a dial tone source, a ring back tone source, means controlled by said operation of said relay for extending a dial tone to said calling station thereby to signal said calling station to commence dialing, a first time-controlled means conditioned responsive to said operation of said relay, a second time-controlled means conditioned responsive to said operation of said relay, said conditioned first time-controlled means becoming effective after a predetermined interval of time for disabling said extension ,of said dial tone and for preparing a circuit to extend a ring back tone to said calling station, said conditioned second time-controlled means becoming efiective after a further predetermined interval of time, and means controlled by said effective second time-controlled means for completing said prepared circuit to extend said ring back tone to said calling station.

11. In a radio telephone system, a station including an antenna, a radio receiver, a radio transmitter and listening means, said listening means having two operating positions, means connecting said receiver to said antenna, means controllable from one of said positions of said listening means for activating said transmitter to develop a radio frequency carrier, means controllable from said second operating position of said listening means for switching said antenna from said receiver to said transmitter, means responsive to a received radio frequency carrier over said receiver for disabling said transmitter activating means to prevent activation of said transmitter should said station operate said listening means to said one and said second operating positions at this time to initiate an outgoing call, means responsive to modulations of said received carrier for signalling said station, means responsive to said modulations of said received carrier for preparing a circuit to re-establish said disabled transmitter activating means, means responsive to said station answering said signalling by operating said listening means to said one operating position for completing said prepared circuit to re-establish said transmitter activating means, said re-established transmitter activating means thereupon causing said transmitter to develop a radio frequency carrier, said switching means responsive to said station operating said listening means to said second operating position for switching said antenna from said receiver to said activated transmitter to establish said transmitter radio frequency carrier on said antenna.

ROSWELL H. HERRICK.

(References on following me) 

